Experimental data up to 463.1 K and 269.14 MPa are revealed for binary and ternary mixtures of poly(phenyl methacrylate) [P(PhMA)] + carbon dioxide (CO2) + phenyl methacrylate (PhMA) and P(PhMA) + CO2 + dimethyl ether (DME) systems. The cloud-point pressure for the P(PhMA) + CO2 + PhMA system is measured with the variations of temperature, and PhMA weight fraction of 39.4, 45.8, 54.2, 59.9, and 62.1 wt %. In 62.1 wt % PhMA to the solution of P(PhMA) + carbon dioxide, the cloud-point phase behaviors are shown the typical lower critical solution temperature (LCST). In addition, the effect by cosolvents concentration for the P(PhMA) + CO2 + DME system is investigated at temperature to 453.9 K and pressure range from 52.24 to 80.86 MPa. The cloud point curve for P(PhMA) + CO2 + DME systems is shifted from LCST region to upper critical solution temperature (UCST) region according to the increase of DME concentration. We report experimental data of the PhMA + CO2 system at high pressures range from 6.24 to 24.90 MPa and at several temperatures, that is, 313.2, 333.2, 353.2, 373.2, and 393.2 K. The experimental results are correlated by the PengRobinson model with the van der Waals one-fluid mixing rule. Overall, group contributions methods estimate the critical properties for used chemicals in this study.